As a conventional exhaust manifold branch collecting portion, for example, Japanese Laid-open Patent Application No. 7-119458discloses to arrange a noise/heat insulating plate provided with a nonwoven fabric, such as glass wool, around the outer periphery of the branch collecting pipe, for the purpose of isolating unusual noise derived from exhaust pulsation, that is, vibrations resulting from a flow of the exhaust gas synchronized with combustion at the engine or for the purpose of preventing as a heat insulation measure the heat quantity of the exhaust gas flowing through the pipe from being discharged to the outside. Further, the temperature of exhaust gas grows higher and higher due to regulations of exhaust gas, and the exhaust manifold branch collecting portion is liable to break because of the pulsation of the exhaust gas. For this reason, a countermeasure has been taken, such as to increase the thickness of the metal plate, by which the exhaust manifold is formed.
However, because the noise/heat insulating plate is formed by a metallic base material, a nonwoven fabric, and a wire mesh and is complicated in structure, there are drawbacks in that the production thereof is difficult and the production cost becomes higher.
In view of the above, the purpose of the present invention is to provide a structure of an exhaust manifold branch collecting portion which is easy to manufacture and which can reduce the cost, by way of preventing, with a simple structural arrangement, the occurrence of unusual noise resulting from exhaust noise that is based on vibrations of the pipe wall due to the flow of exhaust gas and the exhaust pressure and preventing the occurrence of unusual noise derived from vibrations of spatters well as improving the durability of the exhaust manifold.